1. Field of the Invention
The present invention relates to a data filtering apparatus. More particularly, the invention relates to an apparatus and a method for filtering sections transmitted by digital broadcasts.
2. Description of the Related Art
There exist standards exemplified by MPEG-2 that define the transmission of transport streams (TS) of digital broadcasts. According to such digital broadcast standards, video and audio data are put into transport stream packets in the packetized elementary streams (PES) format before being transmitted. The data other than the video and audio data, such as tables and messages, are placed in transport stream packets in the section format when transmitted.
When acquiring desired table or message data from the received transport stream, a digital broadcast receiver or the like may typically perform a two-step filtering process using packet filters and section filters. That is, a packet filter first selects a packet that contains a desired session from the transport stream and extracts the section from the payload of the selected packet. Then a section filter extracts the section data constituting the desired table or message from the extracted section.
Under operational guidelines of the digital broadcast standards, the above-mentioned digital broadcast receiver is required to have a plurality of packet filters and a plurality of section filters. Also, the digital broadcast receiver is required to connect a plurality of section filters to the same packet filter. Furthermore, when connecting the filters, the digital broadcast receiver needs to meet the following two filter connection requirements: First, it is required that any one packet filter be allowed to connect with any number of section filters. Second, it is required that any section filter be allowed to connect with any packet filter.
Traditionally, the above filter connection requirements have been met by the technique of assigning a connection information register to each of the packet filters, the register indicating connective relations of the packet filter in question to the section filters. Each of these connection information registers has a capacity of as many bits as the number of the configured section filters. That is, if N section filters are provided, then each connection information register needs to have a capacity of N bits. Each of the bits constituting the connection information register corresponds to one section filter. In a given connection information register, a “1” bit corresponds to the section filter designated to connect with the packet filter to which the register is assigned.
In the above-described traditional setup, however, the bit capacity of the connection information registers as a whole increases inordinately with a growing number of the packet filters and section filters being configured. This may typically lead to such problems as higher costs due to an expanded scale of circuitry.
Ordinarily, the above problems are circumvented by the technique of limiting the range of section filters that can connect to one packet filter. This technique is intended to make the number of the bits constituting each connection information filter smaller than the number of the configured section filters, thereby suppressing the increase in the bit capacity of the connection information registers as a whole. The scope of limiting the range of the section filters is determined typically by taking into consideration a maximum allowable number of section types (tables or messages) that can be transmitted using a single transport stream packet under the current state of the art. According to this technique, the limitation of the range of the section filters is accompanied by an arrangement that allows the center bit position of the connection information register to correspond to the central section filter in the array of the configured section filters (e.g., see Japanese Patent Laid-open No. 2005-333474).